The first three-dimensional visible light invisibility cloak

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Researchers at the University of Rochester are reporting that they’ve built the first invisibility cloak that works in three dimensions, viewed from a range of angles, across the full spectral range of visible light. As you can see in the photo above, and in the video below, the invisibility effect is rather effective — and, importantly, it creates very little “telltale” distortion that usually accompanies such early attempts at cloaking (the grid lines are perfectly straight and not magnified/minimized). Best of all, though: You can make this particular kind of invisibility cloak yourself!

Unlike other cloaking devices we’ve covered in the past, Rochester’s invisibility cloak is fashioned out of good old lenses — four of them, to be precise. When the lenses are arranged correctly (as dictated by their focal lengths), they create a region of invisibility. The caveat, of course, is that the observer needs to be looking through the lenses (up to an angle of 15 degrees off-center) — but, you can make the lenses as large as you like, so you can still do a pretty good job of making things disappear. Because these are just your standard lenses — like you might find in your spectacles or DSLR — they work across the entire visible light spectrum, and also a few other frequencies as well. The grid lines behind the object show that the very little distortion is introduced by the lenses, meaning the quality of invisibility is quite high.

Rochester’s invisibility cloak, with lasers showing you the path of light through the lenses

Rochester’s invisibility cloak is very simple. Basically, the two outer lenses focus the light from a wide area onto two smaller lenses in the middle. As you can see in the diagram below, this setup creates a region where incident light can’t reach the object, and reflected light can’t reach the observer. Somewhat oddly, the region of invisibility is shaped like a hollow cylinder — or a very tall doughnut, if you prefer. Again, if you make the lenses big enough, the cloaked region would be big enough to hide most things — but on a smaller scale, there are not many doughnut-shaped objects that might benefit from invisibility. Except if your dad/dog/kid keeps eating your last doughnut, of course. [Research paper: arXiv:1409.4705 – “Paraxial Ray Optics Cloaking”]

Four-lens invisibility cloak, from University of Rochester. The two outer lenses funnel light through a narrow middle, creating a cloaked region.

While Rochester’s four-lens method won’t be allowing for Harry Potter-style invisibility cloaks any time soon — we still need some kind of wonder or metamaterial for that — there are still some interesting applications. With some particularly fine lenses — perhaps fresnel lenses to reduce the size of the setup — surgeons might be able to use this setup to see through their hands, or car/truck drivers might be able to see through the front and rear pillars of their vehicle.

Funnily enough, the Rochester researcher behind this study — John Howell — is the same guy who last year created a human-scale invisibility cloak for $150 — with his kids. While that “cloak” was made out of mirrors instead of lenses, both solutions have one thing in common: They can both be built from cheap, off-the-shelf components. So, go forth and build your own invisibility cloak! And upload David Copperfield-like illusions to YouTube!

Granted, I didn’t watch the entire video, but every object they placed in the line of sight was just above or just below center, which makes sense otherwise it would block the focal point and then no light would pass through. Even the guy’s hand was really just his fingers, with the gap between being where the focal point is located. Sorry, but this is basically just a “camera trick”, not really cloaking.

massau

at the end of the video they stated that it only cloaks a ring around the centre point.

VirtualMark

Yeah… it’s not exactly a “cloak” is it? More like an invisibility machine. Which isn’t too useful, as people may well tend to notice such a machine, which would give you away.

grand_puba

Very interesting although I wouldn’t call it an “invisibility cloak” even if it is technically true.

Johnny

Can’t hide from heat detection though

Avatar1337

actually IR should bend the same.

james johnson

I was thinking the same thing, but the article went out of its way to stress “visible light” cloak. maybe they cant bend IR spectrum yet?

Avatar1337

It is just regular camera lenses. A camera captures IR. If the lenses wouldn’t, then they would probably absorb it anyway, which means heat detection wouldn’t work anyway :P

Avatar1337

I mean, it is not that this type of cloaking is new. I played around with this as a kid. The only thing that is new perhaps is the parallax solution, where you have very little distortion.

Jeff Vahrenkamp

I have made my own incredibly cheap cloaking device out of household items! *Holds toilet paper roll to one eye and peers through the now cloaked hand… *.

chojin999

I am sorry but this looks like a little kid playing magician thing… far from some serious true cloaking device technology.
So nowadays Universities are wasting precious resources and time for these silly things? That’s disheartening indeed.

XenoSilvano

Definition of the word cloak: ‘that which conceals’.

Based on that definition I could infer that applying foundation or concealer to
the face can indeed also be considered as a form of cloaking.

Magnus Blomberg

Foudation and concealer don’t really conceal they just alter. The face is still detectable. The detector should be detecting the background as if nothing was located in between.

Stelth aircraft aren’t really invisible to radar. They are just radar black. They do not reflect radar sinals back to the source and therefore appear black. Against a radar black background (the sky) however they can be considered invisible.

james johnson

nothing a good thermal camera cant cut through

kroozin

Tough crowd here. I thought it was pretty cool.

Pile of Pooh

Cool… except it’s not. They didn’t invent anything — certainly not a “cloaking device.” Light tricks with mirrors and lenses have been around for thousands of years. This is like somebody strapping a doll to a bird and saying they’ve invented the passenger aircraft.

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